Importance of Switch Debouncing
In electronic design, implementing switch debouncing is crucial to prevent misinterpretation of a single button press by the device sampling the switching waveform. Various methods, both in hardware and software, can achieve switch debouncing. The choice of the best debouncing solution depends on several factors, including the application’s cost, size, processing power, environment, and the type of switch being used.
Debounce Circuit Operation
Many debounce circuits manipulate the duration of a switch press to eliminate interference pulses. However, the current circuit does not alter this duration. Instead, it ensures that the output pulse precisely aligns with the time between pressing and releasing the switch. When switch S1 is pressed, monostable IC1a is triggered through gates IC3d, IC3a, and IC3b. The feedback from IC3a to IC3d guarantees that the monostable cannot be triggered again during the pulse duration.
Clocking Bistable IC2a
After the monostable time has elapsed, bistable IC2a is triggered. If, at this moment, the output of IC3d remains high, the Q output of IC2a becomes high, and the g output turns low. The bistable keeps IC3a and IC3b deactivated. Meanwhile, IC3 transfers the output signal of ICS to the monostable’s reset input. As long as switch S1 stays pressed, the monostable is reset through IC3c. Upon releasing the switch, its contact opens, retriggering the monostable. If the switch remains open for the duration of the monostable time, bistable IC2a is reset after that interval. Should the switch contact close during the monostable time, IC2a remains in the set state.
Setting the Timing Parameters
It is crucial for the monostable time to be longer than the switch’s longest open time during the bouncing period. Additionally, the time constant of R2-C2 must be significantly longer than the monostable time to ensure that the feedback from IC3a to IC3d is available throughout the entire monostable period. The circuit’s current draw is approximately 1 mA.
